This proposal will investigate the use of three related ultrasound techniques for the evaluation of blood flow. These methods will be applied specifically in the assessment of liver hemodynamics in which there are various vascular supplies that provide some complicating factors. In addition, these techniques may provide some additional diagnostic information in the evaluation of liver lesions such as metastasis. Three methods will be tested. Contrast interruption uses transcutaneously applied ultrasound to create high temporal resolution boluses in the vessels following simple intravenous infusion of microbubble-based ultrasound contrast agent. These boluses are created without arterial catheterization and yet provide similar washin-washout. Perhaps even more important is the ability to repeated interrupt the flow of agent for both multiple boluses during continuous IV fusion. Interruption in specific vessels can determine relative flow contribution and be used during other types of perfusion measures. Contrast decorrelation measures the motion of contrast through the ultrasound beam by examining the gradual loss of speckle coherence at a given location. The technique has the property of directly estimating a mean transit time, and at least in preliminary studies, appears to be quite angle independent. With certain modifications, the technique may directly yield perfusion in a real-time imaging application of flow in ultrasound accessible tissues. Finally flash-echo imaging (FEI) is a technique which has already been implemented on a specific scanner. FEI uses higher intensity pulses on ultrasound to destroy contrast agent from the imaging plane and then monitor the rate at which the contrast agent is returned to the tissue being imaged. In contrast to contrast interruption, FEI provides the local blood flow information without selectivity for vascular supply but is a very convenient measurement that is already available. In combination with contrast interruption, considerably more information can be obtained in liver flow than would be possible with FEI alone. The research will investigate the use of these techniques in three specific hepatic applications. 1) Measurement of the relative flow contributions from the hepatic arterial and portal venous systems. 2) Measurement of the mean transit time for these same vascular supplied (The combination of information from 1 and 2 should provide a measure which is analogous to perfusion. And 3) Examine whether differentiation of liver lesions can be achieved. These techniques should not only improve diagnosis of liver disease but should be applicable to a wide variety of hemodynamic measures throughout the body.